Summary of work: An algorithm was developed to correct partial volume effects due to brain atrophy on brain metabolism and blood flow measured with positron emission tomography (PET) in aging and Alzheimer's disease (AD). After correction for atrophy, brain glucose metabolic values were still lower in AD patients than in controls. An algorithm to study the effect of brain atrophy on errors in the stereotactic spatial transformation of PET images also was developed. Errors in spatial transformation were higher in AD patients than in controls, and were correlated with dementia severity.